The present invention relates to cameras.
In particular, the present invention relates to film-transporting and shutter-controlling structures for cameras.
The present invention is particularly applicable to cameras where the film is provided with a single perforation for each film frame and where a differential drive is provided for transmitting a drive both to the structure which transports the film and to the structure which cocks the shutter.
It is in general conventional in photographic cameras to provide a drive which is common to the film-transporting and shutter-cocking structure. However, during take-up of the exposed film, when the latter is wound on a take-up spool, the diameter of the film wound on the latter increases with the result that the angle through which the take-up spool must be turned diminishes during build-up of the take-up spool, in order to transport the film from one frame to the next, and as a result the angular increment of the drive to the take-up spool for transporting the film diminishes during winding of exposed film on the take-up spool.
On the other hand, in order to cock the shutter it is essential to provide at all times a turning angle which remains constant.
A conventional solution to the above problem resides in compensating for the difference between the required turning angles by way of a suitable friction clutch which is situated at a suitable location. A further possibility resides in actuating the driven elements in two phases, according to which in the first actuation phase a drive of a given constant increment is provided in all cases, this drive during the first phase serving on the one hand to cock the shutter and on the other hand to transport the film through a given constant distance. During the second phase of the operation with such a construction, after the shutter has been cocked there remains only a suitable further film-transport to transport the film through the required distance. This second phase of the operation thus becomes correspondingly smaller as result of the fact that the required angle of turning of the take-up spool becomes smaller as the film builds thereon.
A further possibility resides in providing, instead of a friction clutch, a clutch which can be engaged and disengaged.
A further disadvantage of the known solutions involving the use of a friction clutch resides in the fact that with such a solution it is necessary to provide a greater amount of energy than with a solution to the problem involving the use of a differential drive. However, when using known differential drives there is the disadvantage that the shutter-cocking and film-transporting operations cannot be precisely determined. The time required for the parts to move during such operations depends upon the frictional relationships between the moving components which are required to be actuated in the camera. This factor is a disadvantage inasmuch as separation of the drives to the film-transporting structure and shutter-cocking structure is, for example, necessary so that it is possible to operate the shutter independently of the film-transport. Such a problem occurs, for example, when making a double exposure.